Iran is escalating its fight with the United Nations nuclear watchdog by accusing its inspectors of slander and presenting sloppy evidence, according to a legal brief compiled by the Islamic Republic and circulated among diplomats days before a key meeting in Vienna.

An outline by the Trump administration would allow Iran to continue enriching uranium at low levels while a broader arrangement is worked out that would block the country’s path to a nuclear weapon.

The future of high-stakes negotiations over Iran's nuclear program remains shrouded in uncertainty as the U.S. and Iran publicly clash over the terms of an interim agreement proposed by the Trump administration that is intended to pave the way for a longer-lasting deal.